Display screen or portion thereof with a graphical user interface having a transitional icon



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface having a transitional icon, illustrating a first image in a sequence that shows our new design;

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof;

FIG. 4 is a fourth image thereof;

FIG. 5 is a fifth image thereof;

FIG. 6 is a sixth image thereof;

FIG. 7 is a seventh image thereof; and,

FIG. 8 is an eighth image thereof.

The broken line showing of the display screen is environmental, and the broken lines form no part of the claimed design.

The appearance of the transitional icon sequentially transitions between the images shown in FIGS. 1-8. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface having a transitional icon, as shown and described. 